1. Field of the Invention
The present invention relates to a power output apparatus including both an engine and a motor as the power source, as well as to a method of controlling such a power output apparatus. More specifically the invention pertains to a power output apparatus having a linkage mechanism that causes the motor to be linked with either one of an output shaft of the engine and a drive shaft.
2. Description of the Related Art
One of the recently proposed techniques is a hybrid vehicle with a power output apparatus mounted thereon, which includes both an engine and a motor as the power source (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 9-47094). A parallel hybrid vehicle is one of the hybrid vehicles. In the parallel hybrid vehicle, the power output apparatus mounted thereon causes part of the power output from the engine to be transmitted to a drive shaft via a power regulation unit and the residual part to be regenerated as electric power. The regenerated electric power may be accumulated in a battery or used to drive the motor, which is the power source other than the engine. The power output apparatus controls the power regulation unit and the motor in the course of transmission of the power and thereby enables the power output from the engine to be converted into an arbitrary combination of the revolving speed and the torque and output to the drive shaft. In the hybrid vehicle, the engine can thus be driven at a selected driving point having a high driving efficiency, irrespective of the required output to the drive shaft. Compared with the conventional vehicle having only the engine as the driving source, the hybrid vehicle desirably saves the resources and has reduced emissions.
The motor in the power output apparatus may be linked with either one of the drive shaft and an output shaft of the engine. In the arrangement of linking the motor with the drive shaft, the driving efficiency is improved in the under drive state where the revolving speed of the drive shaft is lower than the engine speed. In the arrangement of linking the motor with the output shaft of the engine, on the other hand, the driving efficiency is improved in the over drive state where the revolving speed of the drive shaft is higher than the engine speed. These characteristics are ascribed to the circulation of the power discussed below.
The process of power transmission when the motor is linked with the drive shaft is described with reference to FIGS. 13 and 14. In this example, an output shaft or crankshaft CS of an engine EG is linked with a drive shaft DS via a pair-rotor motor CM functioning as the power regulation unit, and an assist motor AM is connected with the drive shaft DS. FIG. 13 shows a flow of power in the under drive condition that converts the power output from the engine EG to a combination of a lower revolving speed and a greater torque and causes the converted power to be output to the drive shaft DS. A power PU1 output from the engine EG is transmitted as a power PU2 having a lower revolving speed by the pair-rotor motor CM. There is a relative slide between two rotors in the pair-rotor motor CM, and electric power is generated according to a revolving speed difference between the two rotors. Part of the power PU1 output from the engine EG is accordingly regenerated as an electric power EU1. The assist motor AM carries out the power operation with the regenerated electric power EU1 to compensate for a deficiency of torque. A resulting power PU3 output to the drive shaft DS accordingly has the required revolving speed and torque.
FIG. 14 shows a flow of power in the over drive condition that converts the power output from the engine EG to a combination of a higher revolving speed and a smaller torque and causes the converted power to be output to the drive shaft DS. The power PU1 output from the engine EG is transmitted as a power PU4 having a higher revolving speed by the pair-rotor motor CM, which carries out the power operation. The assist motor AM applies a load to compensate for a surplus of torque. A resulting power PU5 output to the drive shaft DS accordingly has the required revolving speed and torque. The assist motor AM regenerates part of the power PU4 as an electric power EU2, so as to apply the load. The regenerated electric power EU2 is supplied to the pair-rotor motor CM.
In the under drive condition, the electric power regenerated by the pair-rotor motor CM positioned on the upstream is supplied to the assist motor AM positioned on the downstream in the course of transmitting the power output from the engine EG to the drive shaft DS. In the over drive condition, on the other hand, the electric power regenerated by the assist motor AM positioned on the downstream is supplied to the pair-rotor motor CM positioned on the upstream. The electric power supplied to the pair-rotor motor CM is again supplied as mechanical power to the assist motor AM positioned on the downstream. There is accordingly a power circulation xcex31 in the over drive condition as shown in FIG. 14. The power circulation xcex31 reduces the percentage of the power effectively transmitted to the drive shaft DS to the power output from the engine EG, thereby lowering the driving efficiency of the hybrid vehicle.
The process of power transmission when the motor is linked with the output shaft of the engine is described with reference to FIGS. 15 and 16. FIG. 15 shows a flow of power in the under drive condition, and FIG. 16 shows a flow of power in the over drive condition. The phenomena observed under the condition of linkage of the motor with the output shaft are reverse to the phenomena under the condition of linkage of the motor with the drive shaft. In the under drive condition, an electric power EO1 regenerated by the pair-rotor motor CM positioned on the downstream is supplied to the assist motor AM positioned on the upstream. In the over drive condition, on the other hand, an electric power EO2 regenerated by the assist motor AM positioned on the upstream is supplied to the pair-rotor motor CM positioned on the downstream. There is accordingly a power circulation xcex32 in the under drive condition as shown in FIG. 15, in the case where the motor is linked with the output shaft of the engine. This lowers the driving efficiency of the hybrid vehicle.
By taking into account the above phenomena, a proposed hybrid vehicle has a power output apparatus mounted thereon, which enables the destination of linkage of the motor to be switched between the drive shaft and the output shaft of the engine (for example, the hybrid vehicle disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 10-75501). The power output apparatus has a first clutch that allows engagement and disengagement between the motor and the output shaft of the engine and a second clutch that allows engagement and disengagement between the motor and the drive shaft. When the engine speed is higher than the revolving speed of the drive shaft, the first clutch disengages while the second clutch engages. This causes the motor to be linked with the drive shaft. When the engine speed is lower than the revolving speed of the drive shaft, on the contrary, the first clutch engages while the second clutch disengages. This causes the motor to be linked with the output shaft of the engine. This mechanism ensures the high driving efficiency both in the under drive condition and in the over drive condition.
In the proposed power output apparatus that changes the state of linkage of the motor, for the further improvement of the driving efficiency, the working point of the engine is set along a certain performance line where the highest efficiency of the engine attains, that is, the performance line attaining the optimum fuel consumption of the engine, both in the under drive condition and in the over drive condition.
In the under drive condition, it is accordingly required to raise the maximum load capacity of the motor and increase the maximum electric current of an inverter circuit for driving the motor, in order to ensure a sufficient level of the maximum torque output from the drive shaft.
The object of the present invention is thus to provide a power output apparatus that reduces the maximum load capacity of a motor and decreases the maximum electric current of an inverter circuit for driving the motor, as well as to provide a method of controlling such a power output apparatus.
At least part of the above and the other related objects is actualized by a power output apparatus including an engine with an output shaft, a drive shaft to which power is output, a power regulation unit that is connected with both the output shaft and the drive shaft, regulates power output from the engine with input and output of electric power, and transmits the regulated power to the drive shaft, a motor with a rotating shaft, and a linkage mechanism that selectively links the rotating shaft of the motor with either one of the output shaft and the drive shaft. A performance area, which is defined by a relationship between torque and revolving speed, is divided by a first performance line and a second performance line, which has a higher torque in a predetermined range of revolving speed than the first performance line, into a first area that mainly adjoins to the first performance line, a second area that is interposed between the first performance line and the second performance line, and a third area that mainly adjoins to the second performance line. The power output apparatus of the invention further includes: a performance line selection unit that selects either one of the first performance line and the second performance line as an engine performance line that is used to determine a working point of the engine in the performance area; and a control unit that causes the performance line selection unit to select the first performance line as the engine performance line in the case where a working point of the drive shaft is present in the first area, and to select the second performance line as the engine performance line in the case where the working point of the drive shaft is present in the third area.
The present invention is also directed to a method of controlling a power output apparatus, which includes an engine with an output shaft, a drive shaft to which power is output, a power regulation unit that is connected with both the output shaft and the drive shaft, regulates power output from the engine with input and output of electric power, and transmits the regulated power to the drive shaft, a motor with a rotating shaft, and a linkage mechanism that selectively links the rotating shaft of the motor with either one of the output shaft and the drive shaft. A performance area, which is defined by a relationship between torque and revolving speed, is divided by a first performance line and a second performance line, which has a higher torque in a predetermined range of revolving speed than the first performance line, into a first area that mainly adjoins to the first performance line, a second area that is interposed between the first performance line and the second performance line, and a third area that mainly adjoins to the second performance line. The method of the present invention includes the steps of: (a) selecting either one of the first performance line and the second performance line as an engine performance line that is used to determine a working point of the engine in the performance area; and (b) selecting the first performance line as the engine performance line in the case where a working point of the drive shaft is present in the first area, and selecting the second performance line as the engine performance line in the case where the working point of the drive shaft is present in the third area.
The power output apparatus of the present invention and the method of controlling the power output apparatus select either one of the first performance line and the second performance line as the engine performance line that is used to determine the working point of the engine, in the performance area defined by the relationship between the torque and the revolving speed. Here the second performance line has a higher torque in a predetermined revolving speed range than the first performance line. The performance area is divided by the first performance line and the second performance line into the first through the third areas. In the case where the working point of the drive shaft is present in the first area, the first performance line is selected as the engine performance line. In the case where the working point of the drive shaft is present in the third area, the second performance line is selected as the engine performance line. The first area is included in an area of over drive operation, whereas the third area is included in an area of under drive operation. When the working point of the drive shaft is present in the third area, the power output apparatus is set in the under drive condition. In the under drive condition, the working point of the engine is determined according to the second performance line selected as the engine performance line. The torque output from the drive shaft in the under drive condition is equal to the sum of the torque output from the motor and the torque output from the engine. Application of the second performance line, which has a higher torque in the predetermined revolving speed range than the first performance line, for the engine performance line increases the torque output from the engine. The technique of the invention thus enables the torque (especially the maximum torque) output from the drive shaft to be kept at an equivalent level to the value attained by the conventional technique even when the smaller torque is output from the motor.
The power output apparatus of the present invention and the method of controlling the power output apparatus desirably reduce the maximum load capacity of the motor and decrease the maximum electric current of the inverter circuit for driving the motor, while ensuring a sufficient level of the maximum torque output from the drive shaft in the case of under drive operation. These characteristics advantageously reduce the size of the motor and decrease the manufacturing cost of the inverter circuit.
In accordance with one preferable application of the present invention, the power output apparatus further includes an area determination unit that determines an area, in which a target working point of the drive shaft is present, based on an externally required output. In the case where the first performance line has been selected as the engine performance line, the control unit causes the performance line selection unit to change the selected engine performance line from the first performance line to the second performance line when the area determination unit determines that the target working point of the drive shaft is present in the third area. In the case where the second performance line has been selected as the engine performance line, the control unit causes the performance line selection unit to change the selected engine performance line from the second performance line to the first performance line when the area determination unit determines that the target working point of the drive shaft is present in the first area.
Similarly, in this preferable application of the present invention, the method further includes the steps of: (c) determining an area, in which a target working point of the drive shaft is present, based on an externally required output; and (d) in the case where the first performance line has been selected as the engine performance line, changing the selected engine performance line from the first performance line to the second performance line when it is determined in the step (c) that the target working point of the drive shaft is present in the third area, and in the case where the second performance line has been selected as the engine performance line, changing the selected engine performance line from the second performance line to the first performance line when it is determined in the step (c) that the target working point of the drive shaft is present in the first area.
In the power output apparatus or the method of the present invention having the above application, in the case where the first performance line is currently used for the engine performance line, the selected engine performance line is changed from the first performance line to the second performance line when the target working point of the drive shaft is present in the third area. This arrangement ensures the smooth change of the engine performance line when the state of the power output apparatus is changed from the over drive operation to the under drive operation. In the case where the second performance line is currently used for the engine performance line, the selected engine performance line is changed from the second performance line to the first performance line when the target working point of the drive shaft is present in the first area. This arrangement also ensures the smooth change of the engine performance line when the state of the power output apparatus is changed from the under drive operation to the over drive operation.
In accordance with another preferable application of the power output apparatus, in the case where the first performance line has been selected as the engine performance line, the control unit causes the performance line selection unit to keep the selection of the first performance line as the engine performance line even when the working point of the drive shaft is present in the second area, until the area determination unit determines that the target working point of the drive shaft is present in the third area. In the case where the second performance line has been selected as the engine performance line, the control unit causes the performance line selection unit to keep the selection of the second performance line as the engine performance line even when the working point of the drive shaft is present in the second area, until the area determination unit determines that the target working point of the drive shaft is present in the first area.
In the case where the working point of the drive shaft is present in the second area, which is defined by the first performance line and the second performance line, the currently selected performance line is continuously used as the engine performance line. This arrangement favorably prevents the frequent change of the engine performance line.
In accordance with still another preferable application of the power output apparatus, the control unit causes the linkage mechanism to link the rotating shaft of the motor with the output shaft of the engine in the case where the working point of the drive shaft is present in the first area. The control unit causes the linkage mechanism to link the rotating shaft of the motor with the drive shaft in the case where the working point of the drive shaft is present in the third area.
In this application, the method of the present invention further includes the step of: (c) causing the linkage mechanism to link the rotating shaft of the motor with the output shaft of the engine in the case where the working point of the drive shaft is present in the first area, and causing the linkage mechanism to link the rotating shaft of the motor with the drive shaft in the case where the working point of the drive shaft is present in the third area.
In the power output apparatus and the method of the present invention having the above application, when the working point of the drive shaft is present in the first area, the power output apparatus is set in the condition of over drive operation. The linkage of the rotating shaft of the motor with the output shaft of the engine thus enhances the driving efficiency. When the working point of the drive shaft is present in the third area, on the other hand, the power output apparatus is set in the condition of under drive operation. The linkage of the rotating shaft of the motor with the drive shaft thus enhances the driving efficiency.
In the power output apparatus of the above application, in the case where the rotating shaft of the motor has been linked with the output shaft of the engine, the control unit causes the linkage mechanism to keep the linkage of the rotating shaft of the motor with the output shaft even when the working point of the drive shaft is present in the second area. In the case where the rotating shaft of the motor has been linked with the drive shaft, the control unit causes the linkage mechanism to keep the linkage of the rotating shaft of the motor with the drive shaft even when the working point of the drive shaft is present in the second area.
The method of the above application preferably includes the step of: (d) in the case where the rotating shaft of the motor has been linked with the output shaft of the engine, causing the linkage mechanism to keep the linkage of the rotating shaft of the motor with the output shaft even when the working point of the drive shaft is present in the second area, and in the case where the rotating shaft of the motor has been linked with the drive shaft, causing the linkage mechanism to keep the linkage of the rotating shaft of the motor with the drive shaft even when the working point of the drive shaft is present in the second area.
In the power output apparatus and the method of the present invention having the above application, even when the working point of the drive shaft enters the second area, which is defined by the first performance line and the second performance line, the destination of linkage of the rotating shaft of the motor is not changed. This arrangement favorably prevents the state of linkage of the rotating shaft of the motor from being changed frequently.
In the power output apparatus of the above application, in the case where the rotating shaft of the motor has been linked with the output shaft of the engine, the control unit causes the linkage mechanism to change the destination of linkage of the rotating shaft of the motor from the output shaft to the drive shaft when the working point of the drive shaft exceeds the second performance line. In the case where the rotating shaft of the motor has been linked with the drive shaft, the control unit causes the linkage mechanism to change the destination of linkage of the rotating shaft of the motor from the drive shaft to the output shaft when the working point of the drive shaft exceeds the first performance line.
The method of the above application preferably includes the step of: (e) in the case where the rotating shaft of the motor has been linked with the output shaft of the engine, causing the linkage mechanism to change the destination of linkage of the rotating shaft of the motor from the output shaft to the drive shaft when the working point of the drive shaft exceeds the second performance line, and in the case where the rotating shaft of the motor has been linked with the drive shaft, causing the linkage mechanism to change the destination of linkage of the rotating shaft of the motor from the drive shaft to the output shaft when the working point of the drive shaft exceeds the first performance line.
In the power output apparatus and the method of the present invention having the above application, in the case where the rotating shaft of the motor is currently linked with the output shaft of the engine, the destination of linkage of the rotating shaft of the motor is smoothly changed at the time when the state of the power output apparatus is changed from the over drive condition to the under drive condition. In the case where the rotating shaft of the motor is currently linked with the drive shaft, on the other hand, the destination of linkage of the rotating shaft of the motor is smoothly changed at the time when the state of the power output apparatus is changed from the under drive condition to the over drive condition.
In accordance with one preferable embodiment of the present invention having the above application, the power output apparatus further includes an area determination unit that determines an area, in which a target working point of the drive shaft is present, based on an externally required output. In the case where the rotating shaft of the motor is linked with the output shaft, the control unit causes the performance line selection unit to change the selected engine performance line from the first performance line to the second performance line when the area determination unit determines that the target working point of the drive shaft is present in the third area. In the case where the rotating shaft of the motor is linked with the drive shaft, the control unit causes the performance line selection unit to change the selected engine performance line from the second performance line to the first performance line when the area determination unit determines that the target working point of the drive shaft is present in the first area.
In this preferable embodiment, the method of the present invention further includes the steps of: (f) determining an area, in which a target working point of the drive shaft is present, based on an externally required output; and (g) in the case where the rotating shaft of the motor is linked with the output shaft, changing the selected engine performance line from the first performance line to the second performance line when it is determined in the step (f) that the target working point of the drive shaft is present in the third area, and in the case where the rotating shaft of the motor is linked with the drive shaft, changing the selected engine performance line from the second performance line to the first performance line when it is determined in the step (f) that the target working point of the drive shaft is present in the first area.
In the power output apparatus and the method of the present invention having the above application, in the case where the rotating shaft of the motor is currently linked with the output shaft of the engine, the selected engine performance line is changed from the first performance line to the second performance line when the target working point of the drive shaft is present in the third area. The destination of linkage of the rotating shaft of the motor is changed from the output shaft of the engine to the drive shaft when the working point of the drive shaft exceeds the second performance line. This arrangement minimizes the difference between the revolving speed of the drive shaft and the revolving speed of the output shaft of the engine, thereby enabling the destination of linkage of the rotating shaft of the motor to be smoothly changed. In the case where the rotating shaft of the motor is currently linked with the drive shaft, on the other hand, the selected engine performance line is changed from the second performance line to the first performance line when the target working point of the drive shaft is present in the first area. The destination of linkage of the rotating shaft of the motor is changed from the drive shaft to the output shaft of the engine when the working point of the drive shaft exceeds the first performance line. This arrangement also minimizes the difference between the revolving speed of the drive shaft and the revolving speed of the output shaft of the engine, thereby enabling the destination of linkage of the rotating shaft of the motor to be smoothly changed.
In the power output apparatus of the present invention, it is preferable that the first performance line attains a highest efficiency of the engine, and the second performance line attains a maximum torque of the engine at each revolving speed.
Using the first performance line that attains the highest efficiency of the engine improves the driving efficiency of the engine in the state of over drive operation and thereby enhances the driving efficiency of the whole power output apparatus. Using the second performance line that attains the maximum torque of the engine at each revolving speed maximizes the torque output from the engine in the state of under drive operation. This allows a smaller torque to be output from the motor. This arrangement further reduces the maximum load capacity of the motor and decreases the maximum electric current of the inverter circuit for driving the motor.
In the power output apparatus of the present invention, the power regulation unit may include a pair-rotor motor having a first rotor connected with the output shaft of the engine and a second rotor connected with the drive shaft, or alternatively include a generator with a rotor shaft and a planetary gear having three rotating shafts, which are respectively linked with the output shaft of the engine, the drive shaft, and the rotor shaft.
The power regulation unit may have the configuration of electrical distribution with the pair-rotor motor or alternatively the configuration of mechanical distribution with the planetary gear.
Although the technique of the present invention is directly applied to the power output apparatus and the method of controlling the power output apparatus, the scope of the present invention includes a variety of equipment and apparatuses with the power output apparatus mounted thereon, for example, a hybrid vehicle with the power output apparatus.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment with the accompanying drawings.